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Is this true? I think your explanation may be misleading. The two ingredients that are of most concern where gasoline is concerned is octane and hepthane. Of the two, Hepthane is the bang component in the fuel and octane is what regulates how easily the fuel burns . . . the more octane in the fuel, the more controlled the explosion is at higher compression.

For example. In a high performance engine that has been running for a bit, and is therefore at its hot operating temperature, the compression itself can "detonate" the fuel in the cylinder before the crankshaft is in the right position and the spark plug has gone off if there isn't enough octane to control the explosion. These engines need higher octane gas to keep the gas from detonating (knocking) too early in the combustion cycle. The Octane is there to slow the combustion process down.

Best,
josh

Quote:

Originally Posted by 7Rage

ok, then forget the numbers.... get the highest octane availabel, besides race fuel

The whole thing with the numbers is the octane, which in lamens terms means how hot it burns. The higher octane gases (in US 89 and 91) burn hotter which makes them more powerful. Engines are designed with a certain fuel usage in mind.

AS far as that design goes: Compression Ratio. Thats why higher end cars get knock whne using low octane gas. It does get the reuired power from the burned fuel.

The terms regualar and premium or whatever is on the pump is a misleading.. Its a sales pitch. MOST people drive an aisian import or mid class american car that takes 87... but to get these people to pay more for gas they call 91 "premium" and people think its better for their cars... not true.

BTW, I use chevron and shell... chevron with techron, and shell has nitrogen enriched fuel... I dont ever use fuel additives...

Higher octane fuel has only one beneficial feature - it allows an engine to run at higher temperatures with more advanced ignition timing under higher levels of compression witout detonating / knocking. Higher octane fuel does NOT have more potential energy and will not make an engine perform better unless that engine is knocking. On modern engines with knock sensors, higher octane fuel may make the engine run better if the knock sensors are retarding the ignition timing, which hinders performance. High octane fuel does not burn cleaner, it does not clean your engine, it does not increase horsepower or torque (unless you are experiencing knock), it does not smell better, it does not increase fuel economy (unless you are experiencing knock) and is not better for the environment. If you buy higher octane fuels for any of the above reasons, STOP!

When should I switch to a higher octane fuel?

First off, never run lower octane fuel than is recommended by the vehicle's manufacturer. If the vehicle manufacturer recommends 89 octane gasoline, this means that the engine has been tuned to perform optimally without detonation on 89 octane fuel. Once you've done some modifications to your engine, the manufacturer's recommended gasoline may no longer suffice. Obviously, if you can hear detonation inside your engine in the form of pinging or "knocking", try a higher octane fuel. You will also need to run a premium grade fuel (91+ octane) if you have a supercharger, turbocharger, or if you have an ignition programmer that advances your ignition timing.

Why is higher octane fuel more expensive?

Higher octane fuels are more expensive because they must go through more refining steps that increases the octane rating. These additional steps do not make the fuel better in any other way.

we all have a misguided sense of knowledge from listening to others... ^^so here's the facts... but we really shouldnt be running 87 in out cars...

I was right about the cars being tuned for a certain octane tho, and since our cars have had vvt and now alot more cars have it (cuz the tech has been around and is cheaper) these engines including some civics need a higher octane...

AND if anyone wants to know why there are different octane numbers around the world...

Research Octane Number (RON)

The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel in a test engine with a variable compression ratio under controlled conditions, and comparing the results with those for mixtures of iso-octane and n-heptane.
Motor Octane Number (MON)

There is another type of octane rating, called Motor Octane Number (MON), or the aviation lean octane rating, which is a better measure of how the fuel behaves when under load, as it is determined at 900 rpm engine speed, instead of the 600 rpm for RON.[1] MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern gasoline will be about 8 to 10 points lower than the RON, however there is no direct link between RON and MON. Normally, fuel specifications require both a minimum RON and a minimum MON.[citation needed]
Anti-Knock Index (AKI)

In most countries, including Australia and all of those in Europe, the "headline" octane rating shown on the pump is the RON, but in Canada, the United States and some other countries, like Brazil, the headline number is the average of the RON and the MON, called the Anti-Knock Index (AKI, and often written on pumps as (R+M)/2). It may also sometimes be called the Pump Octane Number (PON).
Difference between RON and AKI

Because of the 8 to 10 point difference noted above, the octane rating shown in Canada and the United States is 4 to 5 points lower than the rating shown elsewhere in the world for the same fuel. See the table in the following section for a comparison.

Running higher octane than recommended is pointless. In fact hypothetically you can see worse fuel economy. This is because some engines are not capable of advancing timing enough to burn all the fuel and you have unused fuel being exhausted due to octane rating being higher than what the engine is designed for.
Yes the difference would be 99 percent of the time be unnoticeable, but higher octane fuel does not mean more power.

ethanol free 91, or for that matter any other ethanol free grade is real hard to find in my area. I did find a place that sells ethanol free gas but when I went there to fill up, the nozzle would not fit into my gas tank. I asked the attendant about this & was told the nozzle is for filling boat gas tanks not cars. I guess I could have gone & bought a funnel that would fit into the tank & then just fill up from the nozzle to funnel but being that it was a fair drive to get to this place & it was going to be to much of a hassle I just filled up with Chevron 91 as I always will when available from now on. When I go back home to Canada in the spring I can find lots of ethanol free 91 but not down here in Florida.